This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This project focuses on the structural and kinetic characterization of mercuric ion reductase. Mercuric ion reductase is composed of two domains, a catalytic core domain that is highly homologous to the FAD containing pyridine nucleotide disulfide reductase family i.e. glutathione reductase and a second domain, a ~69 amino acid N-terminal domain, with sequence homology to metal binding proteins. We are focusing on two aspects: 1) characterization of structural features in the Hg(II) binding pathway that are essential for efficient catalysis and 2) elucidating mechanisms of protein/protein interactions between the catalytic core of MerA and the NmerA domain as well as of core with other proteins of the mercury detoxification pathway including MerB, an organomercurial lyase, and the integral membrane transport proteins, MerT or MerC. We use Chimera to graphically present structures of Hg(II) and other complexes of the catalytic core domain alone and interacting with other small molecular weight proteins like NmerA or thioredoxin. In addition, we use Chimera to assist us in evaluating sites for mutagenesis and examining possible modes for docking between MerA and the other mer pathway proteins.